Pedeir Ceinc y Mabinogi is a set of four loosely connected prose tales preserved in a couple of late medieval Welsh manuscripts, though they must have reached their present form by about 1200. The conventional title translates as ‘The Four Branches of the Mabinogi’, mabinogi being a word meaning very roughly ‘youthful exploits’, or the early achievements of a hero. But this title tells us almost nothing about the stories. Instead of narratives about a hero’s youth, we find complex, grotesque, sometimes dreamlike stories about magical shape-shifting, curses and taboos, blood feuds, love, abuse, incest and betrayal. Some of the characters recur from story to story, though each of the ‘branches’ can be read more or less independently of the others. The stories move bewilderingly from realistic, even humorous, evocations of life in the small Welsh courts of the Middle Ages to moments of bizarre and extreme violence; they contain intense lyrical and elegiac emotion and incomprehensible survivals of what seems to be pre-Christian, pre-Roman mythical themes. The names of many of the leading figures tantalisingly echo names given to the gods in Irish and even Gallic paganism. These stories are an archaeological site in themselves, a many-layered mound of tradition, in the depths of which lie some of the most basic imaginative tools of Indo-European religion and storytelling.

But they are also completely compelling in their own right as stories. They are told with vivid visual detail, irony and wit, realistic dialogue and sheer energy. Since the 19th century, when they were translated by the aristocratic and erudite English wife of a Welsh ironmaster, there have been many good versions of the text; more recently – as Matthew Francis notes in a brief but insightful introduction – there has been a project involving the reworking of the stories as modern novellas by a group of distinguished Welsh writers. Francis has taken a quite different route and produced an extraordinary new rendering in the shape of four long poems that ruminate over the narrative detail, both compressing the stories and allowing their imagery to unfold and flower.

The poems are full of unexpected verbal triumphs. When Francis tells us about the dealings of the Prince of Dyfed with Arawn, King of Annwfn, the Otherworld, he gives the latter’s dominion the name Unland, a brilliant coinage for a realm that is not exactly ‘faerie’ or Hades or anything so familiar, but is rather a sort of mirror universe, an alternative reality (readers of Susanna Clarke’s Jonathan Strange & Mr Norrell will recognise something similar). Arawn is

chief of unrock, unwood, of sheepclouds
and their pasture of vagueness,
suzerain of shades.

And here is Francis describing the first appearance of the numinous and enigmatic Rhiannon – a figure whose origins may lie in the cult of a pre-Roman horse goddess – who cannot be caught by any pursuer, however slowly she seems to be riding:

She is woman and horse. She rides slower than daydreams.
She is what you’ve forgotten, where the time went.
Singleminded as the sun, she rides
always one way, and the air’s
warmed by her passing.

In the second tale, the horrifying episode where the King of Britain’s half-brother systematically mutilates all the horses of the King of the Irish is economically evoked:

He’s running through the town with a knife, from shriek to shriek.
The shrieks make him feel better. Most are not his.

‘Caves of dark heat, where daffodils/bloom with a sigh’ is another strong image in the same story, Francis’s gentle, even wistful register all the more shocking for being used in the account of a child being burned alive.

The fourth branch is possibly the best known of the stories and was the inspiration for Alan Garner’s unforgettable The Owl Service, published in 1967. It is given a slightly different treatment from the other three, with its chief protagonist, the sage and sorcerer Gwydion, introduced as the teller of the tale. Once again, there are strong and unexpected images: a hidden baby squealing like ‘flying bagpipes’; the ‘nightgown body/and hooks of an owl’. The narrative device allows Francis to end the sequence with a direct reference to the beginning, as Gwydion kills the son of the Prince of Dyfed, whom we met on the first page, so that we are taken back to the opening exchange between world and Otherworld, land and Unland – ‘the forested border/of what can’t be true’, which is (in the poem’s closing line) ‘where stories begin’.

Francis admits to leaving out some episodes, but generally gives an intensely sustained and full account of these disturbing stories. I have to confess to missing one episode in particular: that in which the severed head of the giant King Bran entertains a group of companions at table for decades, making them forget all the sufferings they have experienced, until one of them opens a window westwards and memory returns. Francis alludes to this:

The head is there most of the time now.
They can hear it muttering
to some unseen friends.
The air is too harsh for it.
It wants the moist earth.

But we lose something here: the magical powers of the severed head suggest something of the uncanniness of storytelling and poetry overall, an unheimlich quality that in various ways quite a lot of this material points to, as does a great deal else in medieval Welsh verse and prose. It would be unfair, though, to complain too loudly. Francis’s version of the stories does a superb job of bringing into focus just this uncanniness: the sense of the pervasive shadow of Unland, which is both a liberation from the prosaic and a realisation of uncontrollable danger, the ‘forested border’ and ‘swirling place’ at the edge of vision.